Diagnosis process of vacuum failure in a vacuum chamber

ABSTRACT

A quick set of procedures for diagnosing the cause of a failure in a vacuum system having a pump and a chamber is disclosed. If the base pressure of the system has failed, but the rate of rise has not, then the most likely cause of the failure may be in the pump. If the rate of rise has failed, but the base pressure has not, then the most likely cause of the failure may be in the chamber. If the base pressure and rate of rise have both failed, then the most likely cause of the failure is in the chamber, but there is a slight chance of a failure in the pump. Measurements of the partial pressures of certain residual gases in the system may indicate a leak in the system. Measurements of the partial pressures of certain residual gases while tuning off and on the lamps in the system may indicate a leak in the lamps. Measurements of the partial pressure of helium or other relevant gas, while moving a source of helium around the outside surface of the system, may determine the location of a leak.

FIELD OF THE INVENTION

The present invention relates generally to diagnosing, ortroubleshooting, problems or failures in vacuum systems. Morespecifically, the present invention relates to a method for quicklydetermining the location or cause of a failure in the ability of avacuum system to create or maintain a desired vacuum setpoint pressurefor the manufacturing of silicon wafers.

BACKGROUND OF THE INVENTION

A silicon wafer is the material on which integrated circuit (IC) chipsare made. The manufacturing of IC chips requires a very high-vacuumenvironment. A suitable high-vacuum environment may be created with aproperly designed and manufactured vacuum system. Vacuum systems for themanufacturing of IC chips on silicon wafers are generally known. Thereare many associated parts to a vacuum system, but it can generally bedescribed as having two main sections: the pump and the chamber. Thesetwo sections are generally divided by a gate valve, which seals the twosections off from each other.

After assembling a vacuum system, the vacuum system is tested at a highvacuum setpoint pressure at least as high as the vacuum that it will beexpected to achieve when actually manufacturing IC chips on siliconwafers. The vacuum test essentially qualifies the system to be operatedat pressures up to the high vacuum setpoint pressure. This test may takeup to several hours or days to perform, because the first time that anew system is subjected to a high vacuum, various types of impuritiesand contaminants may be in the system, having been introduced into theparts of the assembly during its manufacture. The impurities andcontaminants will desorb from the surfaces of the interior of the systemwhen subjected to a vacuum. A greater contamination will cause a fasterdesorption rate of gases from the interior surfaces into the interiorspace, and a faster introduction of gases into the interior spaceresults in a longer time to achieve the setpoint pressure. A vacuumsystem may become recontaminated after the first vacuum period, buttypically not to the extent of contamination prior to the first vacuumperiod, so the vacuum test typically takes longer to achieve thesetpoint pressure than do subsequent vacuum periods. The bakeout periodis the time that the system is subjected to a high vacuum, during whichthe impurities and contaminants are desorbed and removed from theinterior of the system, prior to determining the setpoint pressure. Thevacuum test ends when the vacuum of the system reaches the desiredvacuum setpoint pressure and is able to maintain it after the expectedtime for the test has elapsed.

If the vacuum system fails the test, then it will have to be fixed, orthe system will have to be scrapped. These vacuum systems can be veryexpensive, making it very undesirable to have to scrap an entire system.Therefore, the manufacturer of the system will usually try totroubleshoot the problem in order to save the system. Troubleshootinginvolves diagnosing the problem and repairing it.

The base pressure of a vacuum system is the lowest pressure down towhich the system can be pumped. If the base pressure can reach or exceedthe qualifying base pressure, the setpoint pressure, e.g. 6.0×10⁻⁹ torr,then the vacuum system has passed the vacuum test. The base pressure isdetermined by measuring the pressure after bakeout while the pump holdsthe system steady at the ultra high vacuum. If the base pressure has notreached the qualifying base pressure, then the vacuum system has failedthe base pressure test, and troubleshooting may be required.

The rate of rise (ROR) of a vacuum system is the rate at which thepressure inside the chamber rises after the chamber has been isolatedfrom the pump by closing the gate valve. The ROR is measured by closingoff the gate valve and measuring the pressure over a period of time,e.g. 2 minutes. If the pressure rises slowly enough, e.g. at aqualifying ROR of 1.5×10⁻⁶ torr/2 min or less, then the vacuum systemhas passed the ROR vacuum test. If the pressure rises faster than thequalifying ROR, then the vacuum system has failed, and additionaltroubleshooting may be required.

Troubleshooting involves determining the cause of the base pressureand/or ROR failure. Problems arise when the nature of the cause is notreadily apparent. An operator may replace various components of thevacuum system and then retest the system, but without a clear indicationof the nature of the cause of the failure, the operator is leftuncertain over which parts to replace. Indiscriminate or randomreplacement of components and retesting can be both time-consuming andcostly.

It is, therefore, desirable to have a method of diagnosing a vacuumsystem that has a failed base pressure or ROR, that quickly identifiesthe most likely cause of the failure.

SUMMARY OF THE INVENTION

Generally, a method for locating the cause of a failure in a vacuumsystem includes determining whether the base pressure (Pb), or rate ofrise (ROR), or both has failed. This failure information is thencompared with known categories of failure for various components orsections of the vacuum system, including the chamber or the pump.

One category of failure may be: the Pb has failed and the ROR has notfailed. This category suggests that the pump is most likely responsiblefor the failure. Another category of failure may be: the base pressurehas not failed and the rate of rise has failed. This category suggeststhat the chamber is most likely responsible for the failure. A thirdcategory of failure may be: the base pressure has failed and the rate ofrise has failed. This category suggests that the chamber is most likelyresponsible for the failure.

Measurements with an RGA of the partial pressures of certain residualgases in the system may indicate a leak in the system when relativepartial pressures of some of the residual gases are higher than certainothers. Additionally, a bakeout lamp, containing a gas, may be used inthe chamber to heat the chamber during vacuum testing, and a leak fromthe lamp may be indicated when the partial pressure of the same gas thatis in the lamp changes as the lamp is turned on and off.

The cause of a failure in either section may be further narrowed bycomparing the quantities of certain substances in the system, measuredby an RGA, wherein a leak may be indicated when one or more particularsubstances is present in a greater quantity than expected. Additionally,the location of a leak may be determined by moving a source of aparticular gas around the outside surface of either section whilemonitoring the quantity of that substance in the system, so that whenthe quantity of the substance in the system goes up, the location of theleak is determined.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 shows a vacuum system that may be used with the presentinvention.

FIG. 2 is a bar chart of the partial pressures of certain gases within avacuum system that has not failed.

FIG. 3 is a bar chart of the partial pressures of certain gases within avacuum system that has failed.

FIG. 4 is a graph of the partial pressures of certain gases over timewithin a vacuum system that has not failed.

FIG. 5 is a graph of the partial pressures of certain gases over timewithin a vacuum system that has failed.

FIG. 6 is a graph of the partial pressures of certain gases over timewhile turning on the lamps within a system that has not failed.

FIG. 7 is a graph of the partial pressures of certain gases over timewhile turning off and on the lamps within a system that has failed.

FIG. 8 is a graph of the partial pressures of certain gases over timewithin a system having a leak while moving a source of helium around theoutside surface of the system.

FIG. 9 is a flow chart generally summarizing the method of the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A vacuum system passes the vacuum test when its base pressure (Pb) isbelow a qualifying pressure and its rate of rise (ROR) is below anacceptable level. A method for diagnosing the cause of a failure ineither of these parameters for a vacuum system includes a step-by-stepprocedure for narrowing the cause to the most likely component in thesystem by using known behavioral characteristics of such systems undergiven conditions. First, the pass/fail conditions of both the Pb and RORpermit the failure to be placed in one of three categories that indicatean initial suspected general location of the failure. For instance, asituation in which the Pb fails and the ROR passes their qualifyingconditions indicates a Failure Category 1. A situation in which the Pbpasses and the ROR fails indicates a Failure Category 2. Finally, asituation in which both the Pb and the ROR fail indicates a FailureCategory 3. As will be explained in detail below, Failure Category 1suggests a failure in the pump side of the system, and FailureCategories 2 and 3 both suggest a failure in the chamber side of thesystem, but with some variation. After the category, and hence thegeneral location of the failure, is determined, then differentmeasurement techniques with a residual gas analyzer (RGA) will helpnarrow the cause or location of the failure even further. When the causeof the failure is determined with as much specificity as possible, thenthe appropriate action may be taken and the system subjected to a retestto confirm that the problem has been solved.

FIG. 1 generally shows a vacuum system 10, which may incorporate thepresent invention, having a pump 12 mounted on a chamber 14. A gatevalve 16 generally separates the pump 12 and the chamber 14. When gatevalve 16 is open, the pump 12 and the chamber 14 are in communicationwith each other; and when gate valve 16 is closed, the pump 12 and thechamber 14 are isolated from each other.

The vacuum system 10 may be any kind of system that has a pump thatreduces the pressure of the chamber. The described embodiment relates toany vacuum system used in manufacturing IC's on silicon wafers,including a physical vapor deposition (PVD) vacuum system, a chemicalvapor deposition (CVD) vacuum system, an etch vacuum system, etc. Thedescribed embodiment specifically shows a PVD vacuum system, but it isto be understood that the present invention is not restricted to thisone embodiment.

Pump 12 may include a pump for high vacuum pumping. Additionally, aroughing pump is connected through a foreline to chamber 14 in a knownmanner. Except where specifically noted, references to a pump in thisdescription are to the high vacuum pump since the vacuum test describedherein operates in the high vacuum region. High vacuum pumps include acryogenic pump (sometimes called a cryopump), a turbomolecular pump, anda getter pump. In the following description, the invention is describedas including a cryopump; however, it should be understood that any ofthe other types of high vacuum pumps could be used in accordance withthe present invention.

When gate valve 16 is open, the pump can pump down chamber 14 andmaintain both sections in a high vacuum. When gate valve 16 is closed,the pump will usually continue to try to maintain the high vacuum; butsince it is cut off from its pump, the vacuum in chamber 14 has nothingto maintain it, so the pressure in the chamber can rise if there is asource for gases to enter it. In fact, it is expected that small amountsof gases may continue to desorb from the interior surfaces of thechamber causing a normal rise in the chamber pressure when the gatevalve is closed. A failure in chamber 14, however, may cause itspressure to rise unacceptably.

Chamber 14 may include an ion gauge, not shown, for measuring the lowpressures in the chamber 14 at which most other gauges cannot operate.The ion gauge may also show the change in pressure over time. When gatevalve 16 is open, the ion gauge shows the pressure in both chamber 14and pump 12. When gate valve 16 is closed, the ion gauge shows thepressure only in chamber 14.

Chamber 14 may also include a set of bakeout lamps, not shown. A typicalbakeout lamp contains 99% Ar and 1% N₂. The lamps may be used duringbakeout and during actual manufacturing of IC's on the wafers.

Vacuum chambers typically have a lid for an operator to access theinterior of the chamber. The lid is typically sealed to the chamber withan O-ring. An O-ring, however, does not provide the best seal possiblefor a vacuum chamber, because water vapor and other gases can permeatethrough an O-ring into the vacuum chamber. There are other ways to seala vacuum chamber that provide a much better seal, but these other waysrequire much more time to open and close the vacuum chamber, which isunacceptable in commercial uses, where speed is important. Therefore,vacuum chambers used in the semiconductor industry accept the O-ringseal. The fact that water vapor can permeate through an O-ring seal willbe used in one of the diagnostic steps described below.

As stated briefly before, the first step to quickly diagnosing a failurein a vacuum system is to determine to which of three categories thefailure corresponds. The categories depend on whether the base pressureor the rate of rise or both has failed. These diagnosis procedures areperformed after the vacuum test and with a room-temperature vacuumsystem 10, so that every system is measured under the same standardcriteria.

When a vacuum system 10 has a leak, ambient air is entering the systemonly to be pumped back out again by the pump. If the leak is smallenough, then the pump can keep up with it and maintain the base pressureat the qualifying pressure. Sometimes, however, the leak will be toogreat for the pump and the base pressure will not reach the qualifyingpressure. A typical qualifying pressure for a PVD chamber is about6.0×10⁻⁹ torr or less.

When there is a leak in pump 12 or gate valve 16, then the rate of risewill provide no indication thereof, since rate of rise is determinedwhen chamber 14 is sealed off from pump 12 or gate valve 16. Therefore,the only indication of a leak on the pump side may be a failure in thebase pressure. A failure in the base pressure with no failure in therate of rise is Failure Category 1, and indicates the failure was causedon the pump side of vacuum system 10.

When the pump is operating slowly or inefficiently, then the vacuumsystem may not reach its qualifying pressure, so the system will show afailure in its base pressure. The rate of rise may still meet thespecification, since it does not directly depend on the conditions onthe pump side. Therefore, a slow or inefficient pump may present aCategory 1 failure. If the pump has been operated properly, however, itwill not be very likely to fail, so the more likely cause of a Category1 failure is a pump-side leak as described above.

When the ion gauge is contaminated and not working properly, it may reada pressure that is much higher than the actual pressure. Thus, in anultra-high vacuum range, an ion gauge failure may falsely show a failedbase pressure. The rate of rise will not be affected by an ion gaugefailure, since the ion gauge may still show the relative change inpressure, although the indicated pressures are off scale. Therefore, afailed ion gauge may present a Category 1 failure. With current bakeoutprocedures, however, it has become very unusual for an ion gauge tobecome contaminated, so a failed ion gauge is an unlikely cause of aCategory 1 failure.

When chamber 14 has a leak, the base pressure could pass, if the pumpcan keep up with the leak, or fail, but more importantly, the rate ofrise will likely fail. A passing rate of rise for a PVD chamber istypically about 1.5×10⁻⁶ torr/2 min or less. Rate of rise is determinedby closing off gate valve 16. Some amount of rise in the pressuremeasured by the ion gauge is to be expected, because the chamber maystill be outgassing. Outgassing is the desorption of gases from thewalls or structures in the interior of the vacuum system 10 and cancause a rise in the pressure in chamber 14, especially in the earlyperiod after gate valve 16 is closed. When gate valve 16 is closed, thepump has no way to keep up with a leak in chamber 14. Therefore, thereis a high likelihood that the rate of rise will be appreciably higherthan expected when there is a leak in the chamber. On the other hand, ifthe rate of rise passes, then there is very little likelihood of a leakin chamber 14. A failure in the rate of rise with no failure in the basepressure is Failure Category 2, and indicates the failure was caused onthe chamber side of vacuum system 10.

A leak in chamber 14 may be all the way through from ambient air, but itmay also be from the bakeout lamps. The lamps may leak argon into thechamber and cause a higher than expected rate of rise without being toomuch to affect the base pressure. Therefore, a leak in the bakeout lampsmay indicate a Category 2 failure. A test will be described below whichmay confirm or eliminate a leak in the lamps.

When a vacuum system 10 has not been thoroughly tested in the vacuumtest, there may still be a considerable amount of gases in the structureof the vacuum system 10 that have not degassed. In such a case, the rateof rise may be higher than normal. Therefore, an under-baked-out chambermay present a Category 2 failure. If the vacuum test was performed for asufficiently long period of time, however, it would be very unlikely tobe under-baked-out. Thus, some kind of leak in chamber 14 is the mostlikely cause of a Category 2 failure.

A failure in both the base pressure and the rate of rise may hide theexistence of a leak in pump 12, because the failure in the rate of risemakes it very likely that there is a failure in chamber 14, while theremay or may not be a failure in pump 12. The failure of the rate of rise,however, is still an indicator that the most likely cause of the failureis in the chamber 14. In which case, the additional failure in the basepressure may indicate that a leak in chamber 14 is quite substantial. Afailure in both the base pressure and the rate of rise is FailureCategory 3, and it indicates that the chamber 14 is the most likelycause of the failure, while in rare cases there may be a failure in thepump 12. In even rarer cases, the ion gauge may be contaminated.

After the failure category has been determined, and the most likelysection of vacuum system 10 to have failed is determined, it is possibleto narrow the cause of the failure even further. A residual gas analyzer(RGA) can help narrow the cause. Among other things, an RGA can measurethe partial pressures of residual gases in a system. An RGA may accessthe vacuum system's interior through a port in the chamber. The RGA canprovide readings during vacuum testing of the partial pressures ofseveral gases according to their center mass or molecular weight.

The center mass of a hydrogen H₂ molecule is 1+1=2; the center mass ofwater vapor H₂ O is 1+1+16=18; the center mass of nitrogen N₂ is14+14=28; the center mass of carbon monoxide CO is 12+16=28, the centermass of oxygen O₂ is 16+16=32, the center mass of argon Ar is 40; andthe center mass of carbon dioxide CO₂ is 12+16+16=44. The bar chart inFIG. 2 shows the amplitudes of ion current, proportional to the partialpressure, of several gases as may be determined by an RGA for a normalvacuum system with gate valve 16 open and with no failures. The readingsfor H₂ O, N₂, CO, O₂, and Ar are marked. The reading for water vapor isthe highest under normal conditions because water vapor and other gasescan permeate through the O-ring into the vacuum chamber as describedabove. Nitrogen and carbon monoxide are shown together because theircenter masses are the same.

The bar chart in FIG. 3 shows the amplitudes of ion current,proportional to partial pressures, determined by a RGA for a vacuumsystem with a leak. The gases commonly found in air are shown withsignificantly higher amplitudes than in FIG. 2 because air is leakinginto the system. In fact, nitrogen/carbon monoxide and oxygen areactually higher than water vapor. The sign that the vacuum system has aleak is that one or more of these gases or argon are higher than watervapor. This test can be used with a Category 1 failure to confirmwhether there is a leak in the pump side.

If this test shows that there is not a leak in the pump side, then thenext likely cause of the problem is that the cryopump is too slow orinefficient to reduce the pressure in the system to the qualifyingpressure, as described above. In that case, it may be possible toregenerate the pump and see if the problem clears up. Regenerationremoves the captured gases from the cryopump that the cryopump removedfrom the chamber, so the cryopump may be able to operate moreefficiently. If this action doesn't solve the problem, then perhaps theion gauge is contaminated and needs to be replaced; although, that isunlikely.

The above described test with the RGA bar chart when gate valve 16 isopen does not work well with Category 2 and 3 failures since the bestindicator of these failures is a failed rate of rise, which isdetermined with gate valve 16 closed over a period of time. For thesecategories of failure, the RGA may be used to determine the change inpartial pressures of significant gases over a period of time.

FIG. 4 shows the partial pressures of molecules of water vapor,hydrogen, nitrogen, carbon monoxide, oxygen, argon and helium measuredover a time period of approximately ten minutes for a vacuum system 10with no leak. Prior to time 400, gate valve 16 is open, so the pumpmaintains all of the partial pressures at a constant level. Water vaporhas the highest partial pressure because water vapor and other gases canpermeate through the O-ring into the vacuum chamber under ultra highvacuum. At time 400, gate valve 16 closes and stays closed until time402. During this time, the partial pressures are allowed to drift due tothe normal rate of rise in any vacuum system. All of the partialpressures rise, but normally hydrogen and nitrogen/carbon monoxide riseabove water vapor, while helium, oxygen and argon stay below watervapor. At time 402, gate valve 16 is opened again, and the pump canquickly pump the partial pressures back down to their original values.

FIG. 5 shows the partial pressures of the same gases over a time periodof approximately five minutes for a vacuum system 10 with a leak. Priorto time 500, gate valve 16 is open, so the pump maintains all of thepartial pressures at a constant level. Once again, water vapor has thehighest partial pressure. At time 500, gate valve 16 closes and staysclosed until time 502. During this time, the partial pressures drift dueto the rate of rise, but this time the relative partial pressures arevery different from those in FIG. 4, while gate valve 16 was closed.This time, only helium still has a lower partial pressure than that ofwater vapor, while hydrogen and nitrogen/carbon monoxide still riseabove water vapor, but now oxygen and argon also rise above water vapor.The fact that oxygen and argon have risen above water vapor is the signthat there is a leak in vacuum system 10 from ambient air. A hightemperature inside vacuum system 10 may cause a more rapid degassing,resulting in a higher than expected rate of rise, so the temperature ofthe chamber should be checked, too. At time 502, gate valve 16 is openedagain, and the partial pressures quickly return to their originalvalues. Since gate valve 16 is closed between time 500 and time 502, thediagnosis of a leak applies only to chamber 14. Thus, this test can beused on Category 2 and 3 failures to confirm the existence of a leak inchamber 14. If no leak is determined, then the system may just need alonger time for the chamber vacuum test.

If the bakeout lamps are the cause of the failure in chamber 14, thenthey will leak argon into chamber 14. FIG. 6 is a graph from an RGAshowing the partial pressures of several key gases over a period ofabout seven minutes in a vacuum system 10 with good lamps (no leaks) andunder constant ultra high vacuum. Prior to time 600, the lamps are off,and vacuum system 10 is in a steady state. At time 600, the lamps areturned on and the partial pressure for argon goes up for a short timeand then returns to the former steady state. The partial pressures ofthe other gases remain fairly level. When the lamps are turned on, theystart to heat up vacuum system 10. The partial pressure of argon riseswhen the system starts to heat because argon follows the ideal gas law;so as the temperature rises, the pressure rises, too. Also, theincreased heat causes the system to degas more quickly, thus raising thepartial pressure. The partial pressure of argon returns to the formersteady state, because the pump continues to maintain the ultra highvacuum and soon pumps the partial pressure back to normal. This graphshows the expected behavior of the partial pressures for a good vacuumsystem 10.

FIG. 7 shows a graph from an RGA showing the partial pressures of thesame gases as in FIG. 6 under a constant ultra high vacuum for a periodof about seven minutes, but in a vacuum system 10 with lamps that leak.Prior to time 700, the lamps are on and the system is in a steady state.At time 700, the lamps are turned off until time 702. The partialpressure of argon begins to change as soon as the lamps are turned off,but the partial pressure does not return to the same steady state asbefore the lamps were turned off. Instead, the new steady state for thepartial pressure of argon is lower than previously. At time 702, thelamps are turned back on, and the partial pressure of argon quicklyjumps back up to the higher steady state. Such a graph indicates thatthe lamps are leaking argon, and the leak is higher when the lamps areon than when off, thus the two different steady state conditions.Additionally, the fact that argon is getting into the system fromsomewhere is shown by a comparison of FIGS. 6 and 7. The partialpressure of argon in FIG. 6 is about 2×10⁻¹¹ torr, but the partialpressure of argon in FIG. 7 is above 2×10⁻¹⁰ torr, a whole order ofmagnitude higher than the expected partial pressure for a good system inFIG. 6.

After determining that there is a leak in vacuum system 10 from ambientair, it is possible to determine the location of the leak in each of theFailure Categories. FIG. 8 shows a graph from a RGA showing the partialpressures of several important gases in a vacuum system 10 under aconstant ultra high vacuum for a period of about five minutes. Prior totime 800, the system is in a steady state. There is a leak in thesystem, but the pump can hold the system steady. At time 800, thepartial pressure for helium suddenly jumps and rises by almost twoorders of magnitude, as helium is coming in through the leak in thesystem. At time 802, the helium stops coming in through the leak, andthe system quickly returns to the steady state. This condition can occurwhen a source of helium is applied outside vacuum system 10 at thelocation of the leak from ambient air. Thus, the location of a leak invacuum system 10 can be determined by slowly moving the source of heliumaround the outside surface of the system while watching for a rise inthe partial pressure of helium on the RGA. This method can be used forany of the categories of failure when a leak is suspected. Gases otherthan helium may be used.

For a Category 3 failure, if the above diagnosis procedures do notlocate the problem in the chamber, then the vacuum system may have oneof those rare cases in which a Category 3 failure is caused by the pumpside. In this case, the pump may have to be changed.

FIG. 9 shows a flow chart summarizing the method of the presentinvention. Initially, a determination is made as to whether the likelycause of failure is the pump side or the chamber side. This involvescategorizing the results of a Pb and ROR test as shown in block 900.Once the gate valve is opened, the chamber is allowed to reach a Pbwhich is measured and recorded as indicated by step 902. In step 904,the gate valve is closed and the ROR is checked and recorded. Therecorded values for Pb and ROR are compared against predeterminedpass/fail values. Steps 906-910 indicate the categorization according towhether the chamber exhibits a Pb failure (a category I failure), an RORfailure (a category II failure), or both (a category III failure). In acategory I failure (Pb failure), the probable cause is the pump side, asindicated at step 912, which is generally understood to be the pumpand/or the gate valve. Category II and III failures both exhibit an RORfailure and the probable cause of failure is the chamber side asindicated by steps 914-916. The chamber side comprises the chamber body,the ion gauge and any lamps. However, as described above, a chamber sidefailure generally indicates a leak in the chamber body.

Block 918 shows the next phase of the present invention wherein theprobable cause of failure, as determined by block 900, is furtherconfirmed or rejected. For this purpose, the method of the presentinvention uses two distinct tests, one for category I failures andanother for category II and III failures. Step 920 indicates the testfor category I failures. As described above, the gate valve is firstopened and the chamber is pumped down. The partial pressures of N₂, CO,O₂, and Ar are then compared to the partial pressure of water vapor. Thetest for category II and III failures, shown by step 922, is performedwith the gate valve closed after pumping the chamber to its Pb. A fewminutes (approximately two) are allowed to elapse and then the partialpressures of Ar and O₂ are compared against that of water vapor.

After each test in block 918, the results are analyzed to determinewhether a leak is confirmed. In the case of category I failures, wherethe partial pressures of N₂, CO, O₂, and Ar are higher than that ofwater vapor a leak is confirmed. The leak is subsequently isolated bymoving an inert gas source (such as helium) around the pump side asindicated by steps 924 and 926. Where a leak cannot be confirmed thepump may need to be regenerated as indicated by step 932. Ifregeneration is unsuccessful, the ion gauge may need to be replaced asindicated by step 934.

Similarly, category II and III failures are confirmed where the partialpressures of Ar and O₂ are higher than that of water vapor as shown bystep 928. In that case, the leak is isolated by moving an inert gassource around the chamber side as indicated in step 930. Additionally,as indicated by steps 936 and 938, where the chamber is equipped withlamps and only the partial pressure of Ar is greater than that of watervapor, the lamps should be checked for leaks according to the proceduredescribed above. In the rare case where no chamber side leak can beconfirmed for category III failures, the pump may be the source of aleak and should be replaced if necessary.

While the foregoing is directed to the preferred embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims which follow.

I claim:
 1. A method of determining a location and cause of a failure ina vacuum system having a pump having an outside surface and a chamberhaving an outside surface, comprising:a observing a base pressure in thechamber to determine the likely cause of failure to be the pump andobserving a rate of rise in the chamber to determine the likely cause ofthe failure to be the chamber; (b) monitoring a quantity of a firstsubstance in the vacuum system; (c) moving a source of the firstsubstance around the outside surface of the pump or the outside surfaceof the chamber depending on the likely cause of the failure asdetermined by (a); and (d) isolating the leak in the vacuum system to alocation on the vacuum system adjacent the source of the first quantityof the first substance.
 2. The method of claim 1 wherein the firstsubstance is a detectable inert gas.
 3. The method of claim 1 whereinthe first substance is helium.
 4. A method of determining a location andcause of a failure in a vacuum system having a pump having an outsidesurface and a chamber having an outside surface, comprising:(a)determining a base pressure of the system;comparing the base pressurewith a qualifying pressure, a base pressure greater than the qualifyingpressure indicating that the vacuum system has a base pressure failure;determining a rate of rise of the system; comparing the rate of risewith a qualifying rate of rise, a rate of rise greater than thequalifying rate of rise indicating that the vacuum system has a rate ofrise failure; when the vacuum system has a base pressure failure anddoes not have a rate of rise failure, determining the most likelylocation of the cause of the failure to be in the pump; when the vacuumsystem has a rate of rise failure, determining the most likely locationof the cause of the failure to be in the chamber; (b) monitoring aquantity of a first substance in the vacuum system; (c) moving a sourceof the first substance around the outside surface of the pump and theoutside surface of the chamber; and (d) determining the location of aleak in the vacuum system, a rise in the quantity of the first substancewhen the source of the first substance is at a particular location onthe outside surface of the pump or the outside surface of the chamberindicating the location of the leak at the particular location; (e) whenthe most likely location of the cause of the failure is determined to bein the pump, moving the source of the first substance around only theoutside surface of the pump; and (f) when the most likely location ofthe cause of the failure is determined to be in the chamber, moving thesource of the first substance around only the outside surface of thechamber.
 5. The method of claim 4 further comprising:(g) prior to themonitoring step:determining a quantity of at least one second substancein the vacuum system; determining a quantity of a third substance in thevacuum system; and determining whether the cause of the failure is aleak by comparing the quantity of the at least one second substance withthe quantity of the third substance, a greater quantity of the at leastone second substance than of the third substance indicating that thecause of the failure is a leak.
 6. The method of claim 5 wherein thesecond substance is a detectable gas selected from the group consistingof nitrogen, carbon monoxide, oxygen and argon.
 7. The method of claim 6wherein the third substance is water vapor.
 8. The method of claim 4further comprising:(g) replacing the pump when step (a) determines themost likely location of the cause of the failure to be in the chamber,but steps(b), (c), (d) and (f) do not determine the location of a leak.9. A method of determining a location and cause of a failure in a vacuumsystem having a pump and a chamber and a lamp disposed within thechamber, the method comprising:(a) monitoring a quantity of a substancein the vacuum system; (b) turning off the lamp for a first time period;(c) turning on the lamp for a second time period; and (d) determiningthat the lamp is leaking the substance into the chamber where a higherquantity of the substance is monitored during the second time periodthan during the first time period.
 10. The method of claim 9 wherein thesubstance is a detectable gas and the lamp comprises the detectable gas.11. The method of claim 9 wherein the substance is argon and the lampcomprises argon.
 12. The method of claim 9 further comprising:(e) priorto step (a):determining a base pressure of the system; comparing thebase pressure with a qualifying pressure, a base pressure greater thanthe qualifying pressure indicating that the vacuum system has a basepressure failure; determining a rate of rise of the system; comparingthe rate of rise with a qualifying rate of rise, a rate of rise greaterthan the qualifying rate of rise indicating that the vacuum system has arate of rise failure; when the vacuum system has a base pressure failureand does not have a rate of rise failure, determining the most likelylocation of the cause of the failure to be in the pump; when the vacuumsystem has a rate of rise failure, determining the most likely locationof the cause of the failure to be in the chamber; and when the mostlikely location of the cause of the failure is determined to be in thechamber, performing steps (a) through (d).
 13. A method of determining alocation and cause of a failure in a vacuum system comprising a pumpside and a chamber and a lamp disposed within the chamber, the methodcomprising:(a) measuring a first pressure of a first substance in afirst steady state in the chamber; (b) turning on the lamp; (c)measuring a second pressure of the first substance in a second steadystate in the chamber; and (d) determining that the lamp is leaking thefirst substance into the chamber where the first pressure is higher thanthe second pressure.
 14. The method of claim 13 wherein the substance isa detectable gas and the lamp comprises the detectable gas.
 15. Themethod of claim 13 wherein the substance is argon and the lamp comprisesargon.
 16. The method of claim 13 further comprising:(e) prior to step(a):(i) determining a rate of rise of the system; (ii) comparing therate of rise with a qualifying rate of rise, a rate of rise greater thanthe qualifying rate of rise indicating that the vacuum system has a rateof rise failure; and (iii) determining the likely location of the leakto be in the chamber.
 17. The method of claim 16 further comprising:(f)subsequent to (e) and prior to (a):(i) moving the source of the firstsubstance around an outside surface of the chamber; and (ii) isolatingthe leak in the vacuum system to a location on the chamber adjacent thesource of the first substance at which the quantity of the firstsubstance in the vacuum system rises.
 18. The method of claim 13 furthercomprising:(e) prior to step (a):(i) determining a quantity of one ormore second substances in the vacuum system; (ii) determining a quantityof a third substance in the vacuum system; and (iii) comparing thequantity of the one or more second substances with the quantity of thethird substance; and (iv) determining a greater quantity of the one ormore second substances than of the third substance.
 19. The method ofclaim 18 wherein the one or more second substances comprises argon.